Gas turbine engines typically have fuel supply systems for delivering fuel to a combustor, where the fuel is ignited to produce a thrust. In many engines, the fuel is stored in a fuel source, such as a fuel tank, and is drawn out by one or more pumps. The pumps pressurize the fuel and deliver the pressurized fuel to manifolds in the combustor via a main supply line. To control the rate at which the fuel flows through the system, the main supply line may include one or more valves in flow series between the pumps and the fuel manifolds. These valves generally include at least a main metering valve and a bypass valve. The bypass valve may be disposed in a bypass flow line connected upstream of the metering valve for allowing a portion of the fuel flowing in the main supply line back to the inlet of the one or more pumps.
During operation, a flow rate across the main metering valve is determined in order to establish whether the bypass valve should be used or whether to change the flow rate of the fuel through the system. In this regard, a position sensor is coupled to the main metering valve. The position sensor can be a linear variable differential transformer and can include a core surrounded by primary and secondary windings. The core is typically coupled to the main metering valve and moves linearly through the primary and secondary windings. When the flow rate across the main metering valve changes, the core changes position relative to the primary and secondary windings and the change in position is then communicated to a controller. The controller determines whether to send a signal to increase or decrease the flow rate across the main metering valve.
Although the aforementioned linear variable differential transformers are adequate for use in conventional engines, they may be improved. For example, in some engines, the linear variable differential transformer components are exposed to a harsh environment in front or around the engine and may be more susceptible to corrosion. Additionally, as engine power output demands increase and engine operating temperatures increase, the linear variable differential transformer is subjected to high-temperature air around the LVDT (e.g., environmental temperatures up to 500° C.). The high-temperature environment may decrease the winding and termination reliability of the linear variable differential transformers causing frequent need for replacement and increase in maintenance costs of the engine. In addition high temperature introduces measurement error that must be accounted for through component design and/or signal conditioning.
Accordingly, it is desirable to have an improved linear variable differential transformer that may be more corrosion-resistant than conventional linear variable differential transformers. In addition, it is desirable to have a linear variable differential transformer that can be employed in environments that may be subjected to environmental temperatures up to 500° C. Furthermore, other desirable features and characteristics of the inventive subject matter will become apparent from the subsequent detailed description of the inventive subject matter and the appended claims, taken in conjunction with the accompanying drawings and this background of the inventive subject matter.